A dose distribution measuring device is a device for measuring the dose distribution of radiation emitted from an object or measurement region, the distribution of a radioactive substance contained in the object or measurement region, or the angular distribution of a radiation dose at a specific position, a so-called spatial dose.
A dose here generally means the type, energy, or count of radiation, the dose of radiation calculated in consideration of influence on the human body, or the radioactivity or content of a radioactive substance, and is expressed in a unit such as CPM (Count Per Minute), CPS (Count Per Second), CPH (Count Per Hour), Ci (Currie), Bq (Becquerel), Gy (Gray), rad (Rad), rem (Rem), Sy (Sievert), or Rm (Roentgen).
In addition, since there is no effective lens or mirror for radiation, a dose distribution measuring device including a pinhole, coded mask, or collimator has been conventionally used to measure the dose distribution of radiation emitted from an object or measurement region (see patent literatures; Japanese Patent Application Laid-Open No. 2001-305233, Japanese PCT National Publication No. 2008-523405 and Japanese Patent Application Laid-Open No. H10-319122.
However, in order to secure an effective contrast for a dose distribution, a pinhole, coded mask, or collimator is formed from a small hole formed in a thick metal plate made of a metal with a very high specific gravity such as lead. In addition, a radiation detecting two-dimensional array which measures a dose distribution is incorporated in a radiation shielding box having as its part a pinhole, coded mask, or collimator. This arrangement has posed problems that, for example, the overall apparatus is very heavy and it is difficult to, for example, move, install, and operate the apparatus.
In addition, it is necessary to detect a small amount of radiation having passed through the small hole formed in such a thick metal plate. In order to obtain a detection signal with a high SN ratio, therefore, it is necessary to integrate and measure detection signals over a long period of time.
Furthermore, owing to the structure in which the radiation detecting two-dimensional array is installed in the radiation shielding box, in order to obtain a spatial dose at a measurement position, it is necessary to separately perform measurement using a spatial dose measuring device.